Interactions between environmental and genetic factors have been implicated in the etiology of breast cancer. In particular, several studies have suggested that the type of genetic damage observed in human breast tumors may be influenced by exposure to chemical toxicants. However, few attempts have been made to compare the ability of breast tissue to metabolize chemical carcinogens with the types of mutations observed at critical oncogenic loci. To better understand the etiology of breast carcinogenesis and determine the role of gene/environmental interactions in determining individual susceptibility to breast cancer formation, a prospective case-case study design will be utilized to compare mutations in the p53 gene with the genotype of affected cancer patients for 4 metabolic enzymes (CYP1A1, GSTM, GSTT, and GSTP) that play key roles in the metabolism of human environmental carcinogens. We hypothesize that those breast cancer patients containing either specific alleles of CYP1A1 that enhance the metabolic activation of environmental toxicants or genotypes of GSTs that would result in less detoxification will be more likely to have accrued genetic damage at the p53 locus, and that combinations of alleles that increase the burden of reactive electrophiles will be more susceptible to tumor initiation. Tumor tissue samples will be analyzed for genetic alterations in p53 by SSCP and gene sequencing analyses. DNA obtained from blood will be genotyped by PCR-RFLP to determine if patients harboring genetic damage to p53 more frequently exhibit metabolic genotypes that increase formation of reactive electrophiles from invironmental toxicants. A prospective study design will allow use of a questionnaire to identify other potential factors (including smoking, diet, occupation, race, and reproductive history) that may modify the association between genotype and mutations to p53. As mutation at p53 has been implicated in poor patient prognosis, these studies should aid in identifying those patients at risk for damage to key regulatory genes that play a role in the pathogenesis of breast cancer, and will further our understanding of the etiology and risk factors for this disease.